Tableting machines for the compression of powders into tablets have been known for a great many years, and it has been conventional to convey said powders by gravity from a source of supply, such as a large tank or hopper located above the tableting machine, sometimes through secondary hoppers, into that part of the tableting machine wherein such powders are compressed into tablets.
It has been recognized for years that the output of existing tablet machines has been limited by the speed at which the powder could be moved from the supply thereof to the die cavities of the tableting machine without adversely affecting the quality of the tablets. It is the purpose of the present invention to improve powder flow and thus improve the output of such machines.
It has long been known that some powders are inherently of a somewhat cohesive nature and hence it has been the practice in many cases first to granulate these powders to render them more flowable and thereby prevent, or at least minimize, their tendency to become compacted, plugged or bridged within the feed system and thereby at least to restrict, if not stop, the powder flow.
By way of example, some powders must contain so much medication that the binders and/or other inert excipients must be minimized to avoid a tablet of uningestible size. The nature of some medications is such that the lubricants, binders and/or disintegrants, for example, required with the medicated powders create severe flow problems which have previously prevented direct compaction of these mixtures, at least at a commercially acceptable rate. Also, the nature of some powdered medications is such that they severely limit the choices of excipients to those which display bad flow characteristics, even when they are mixed with the medication.
The aforesaid problems arising out of poor flow characteristics are also found in other fields, such as the tableting or compaction of candy, soap, sintered metal pellets and the like.
It is thus desirable to provide an improved method of handling direct compaction powders so as to eliminate the cost, the further time required, and the danger of variables involved as a consequence of such additional step, namely, the granulation step. However, it is also desirable to improve the flow of certain granules from their source of supply to the tableting machine.
It has been observed in many instances that, where the powders are delivered directly from standard feed hoppers to the tableting machine for compression thereby into tablets, the machine can form tablets from such powder much more rapidly than the powder can be delivered to the tableting zone. Accordingly, to prevent powder starvation, due to interruption of proper powder flow, and consequent tablet weight variation, it has been necessary to run the tableting machine at a rate less, often much less, than it is inherently capable of operating. In some instances, the tableting machine has been able to operate at only about 25 percent of the speed of which it is capable because of said limitations in the delivery capacity of the powder feeding system.
Related to, but distinguishable from, this problem is the necessity of balancing the powder feed to the demand of the tableting machine. While diligent efforts have been made to maintain the tablets as uniform as possible, there is nevertheless some slight variation therein which some tableting machines are programmed to sense and compensate. However, where machines lack these compensating features, it was found that tablet weight variations were often created by corresponding, uncontrolled variations in the weight of the powder backed up in the feeding system. Material variations in the weights of medicinal tablets often produce unacceptable variations in the dosage of such tablets. Thus, there has been a need for a feed system by which to provide prompt adjustments in the amount of the powder being provided by the feeding system, particularly where such machines do not have powder quantity or weight sensing devices.
It was found that the desired control and adjustment of the powder in the feed system could be more adequately achieved by urging the powder from the primary source by a successive plurality of bursts of entraining fluid, normally air.
Therefore, the objects of the invention include:
1. To provide a method and apparatus for feeding powder from a primary source, such as a relatively large hopper, to the intake means of a tableting machine, said feeding apparatus being able to effect a high volume of powder transmission with a minimum of compacting, bridging or interrupting the flow of the powders either within such feeding apparatus itself or within the intake mechanism of the tableting machine.
2. To provide apparatus, as aforesaid, which will effectively reduce, if not eliminate, the pressure created by the air-powder stream before it reaches the tableting machine so that the air itself will not act as a compacting force upon the powder.
3. To provide apparatus, as aforesaid, which will automatically adjust for momentary differentials between the demand of the tableting machine for powder and the delivery of the powder by the feeding system, so as to maintain a constant supply of said powder with minimum variations in the amount of powder in the feed system.
4. To provide apparatus, as aforesaid, which will insure that the powder is delivered to the tableting dies at a high level of uniformity in density and a low level of both static and velocity pressure.
5. To provide apparatus, as aforesaid, which will be compatible with available equipment and which can be easily installed thereinto as modifications thereof.
6. To provide apparatus, as aforesaid, whose components can be selected through a broad range of sizes and other specific details.
7. To provide apparatus, as aforesaid, which will be relatively easy to install, operate, adjust and maintain.
8. To provide apparatus, as aforesaid, which will have minimal moving parts and, hence, be capable of long and reliable operation with a minimum of maintenance.
9. To provide apparatus, as aforesaid, which is capable of feeding powder having poor flow characteristics, in order to form tablets therefrom by direct compaction.
10. To provide apparatus, as aforesaid, which would be capable of supplying powder to plural machines at the same time from a remote source of supply.
Other objects and purposes of the invention will be apparent to persons acquainted with apparatus of this general type upon reading the following specification and inspecting the accompanying drawings.